The present invention relates to a method and apparatus for converting tidal power into electrical energy and more particularly, the present invention relates to caisson type device having a paddle wheel which may be variably positioned within a tidal stream.
As the moon orbits around the earth, the gravitational force of the moon and sun pull the oceans creating the tides. It is undoubtedly the most powerful active force on earth. An immense amount of energy is inherent in these large bodies of moving water. To harness a small fraction of this energy and convert it into electricity, many innovative methods have been conceived.
The net energy in a tidal stream is very large. When a tidal stream is restricted by two points of land, the velocity is increased considerably, condensing the net energy through the constricting points of land. To extract a significant amount of energy from this relatively slow moving body of water, a large cross-section of the tidal stream needs to be harnessed. The simplest way to achieve this goal is through the use of a large paddle wheel or underwater sail. The energy extracted is directly proportional to the size of the paddle wheel.
For a paddle wheel to operate efficiently, only the lower half of the wheel should be submerged below the surface of the water, leaving the upper half of the wheel exposed to surface elements such as wind and waves. The paddle wheel structure need also contend with surface conditions such as slab ice and floating debris.
A housing may be constructed to protect the paddle wheel(s) but this would add considerable height, cost and complexity to a potential structure. A housing would also elevate the centre of gravity, a characteristic not conducive to stability during tow-out and transportation operations. As well, to protect the paddle wheel from floating debris, the housing would have to protrude below the surface of the water, restricting the flow of water to the paddles.
The most restrictive characteristic of a large structure protruding through the surface of the water is that it creates a barrier against surface ice flow. This can be disastrous, as the force behind a restricted ice flow can be fatal. With river ice, restricting the flow can mean serious flooding upstream. Marine structures that encounter ice are generally designed to minimize resistance. With the type of structure noted above, this would not be possible.
In numerous cases, the fastest (higher energy) tidal streams are found where large bodies of water are fully or partially enclosed by land except for one or more openings to the sea. In a lot of these cases, it would be desirable to link the two or more points of land adjacent to the openings. Often, the depth of water or span at the opening does not make a conventional bridge feasible. The preferred embodiment is intended to generate electricity at these tidal stream openings as well as potentially provide the base foundations for such a bridge.
The original and simplest method of harness sing tidal power was a barrage and paddle wheel. Subsequently, many intricate methods using a differential of water elevations have been devised. In recent years, barrage of coastal waters has elicited considerable public opposition. Barrage restricts recreational activities and commercial traffic. Due to the growing opposition, the focus of harnessing tidal power has shifted to tidal streams and non-coastal barrage systems. This shift has introduced new challenges and obstacles, as tidal streams are generally found in deeper and more treacherous waters. Structures built at such locations are susceptible to ocean storms, slab ice and icebergs. There have been systems developed to harness tidal streams in ice-free locations that are relatively sheltered. Unfortunately, no arrangement capable of withstanding the environmental forces of icebergs, slab ice and severe ocean storm waves has become available.
In the prior art a wide variety of devices have been proposed. Typical of the arrangements is referenced in U.S. Pat. No. 4,717,831, issued Jan. 5, 1988, to Kikuchi. In the document a power generator is disclosed. The generator provides a plurality of paddle wheels fixed in place essentially immovable and exposed without any coverage from debris. It would therefore appear that the Kikuchi system would be vulnerable to damage if used in more extreme environments.
Mayo, Jr., in U.S. Pat. No. 6,208,037, issued Mar. 27,2001, provides a power generating system which is also a permanent structure and is designed for fixture within a waterway. Generally speaking, these systems are cumbersome, expensive and require the use of one or more operators.
U.S. Pat. No. 5,440,175, issued to Mayo, Jr. et al., Aug. 8, 1995, discloses a river bridge electrical generator unit. This unit is, similar to those discussed above, for barrage and thus does not overcome the limitations outlined in the discussion herein previously.
Other references in the realm of the present invention include U.S. Pat. Nos. 5,430,332, 4,511,808, and 4,001,596.
In view of the state of the art in this niche of civil engineering, there exists a distinct need for a versatile, durable and relocatable tidal power system which is absent the disadvantages connected with the current devices. The present invention addresses the requirements for a high-performance system for efficient extraction of the energy inherent in tides.
One object of the present invention is to provide a caisson for creating electrical power from a tidal stream, comprising:
a body having an inlet and an outlet to allow the passage of water there through;
a compartment extending between the inlet and the outlet;
at least one paddle wheel rotatably mounted within the compartment for contact with incoming water;
means for pressurizing the compartment to reduce the volume of water present in the compartment when the caisson is submerged in the stream;
pump means connected with the at least one paddle wheel; and
generator means connected to the pump means for generating electrical power.
The generated power may also then be used to create hydrogen for hydrogen fuel cells.
A further object of the present invention is to provide a method of converting mechanical energy from tidal motion to electrical energy, comprising:
providing a movable paddle wheel within an enclosure, the enclosure having an inlet and an outlet for facilitating contact of the paddle wheel with a tidal stream;
connecting the paddle wheel to means for converting energy created during rotation of the paddle wheel to electrical energy;
positioning the paddle wheel into contact with the stream;
selectively pressurizing the enclosure to alter the level of submersion of the paddle wheel in the water within the enclosure; and
collecting energy created from the tidal motion of the paddle wheel.
Having thus described the invention, reference will now be made to the accompanying drawings illustrating preferred embodiments.